Method of regenerating sodium plumbite solution



METHOD OF REGENERATING SODIUM PLUMBITE SOLUTION Filed NOV, 11, 1953 2 Sheets-Sheet l f 22 30 I I 24 Zmventofs F/Emfz/ck W- 5704 5 JAMES M 5/1 228/50 Nov. 26, 1935. F, w. STONE ET AL METHOD OF REGENERATING SODIUM PLUMBITE SOLUTION 2 Sheets-Sheet 2 Filed NOV. 11, 1955 .E W E m n E t a Patented Nov. 26, I935 ETED STAT METHOD OF REGENERATING SODIUM PLUMBITE SOLUTION Frederick W. Stone and James N. Garrison, Cleveland, Ohio Application November 11, 1933, Serial No. 697,648

3 Claims.

This invention relates to an improved method of regenerating spent sodium plumbite or doctor solution and the present application contains subject matter in common with our United States patent application, Serial No. 650,292, filed January 5, 1933.

Sodium plumbite solution is principally used for chemically treating or sweetening petroleum products, principally gasoline and kerosene. The sodium plubite NazPbOz) converts certain disagreeable smelling sulphur compounds and mercaptans to other compounds which are not disagreeable and also removes some of the sulphur compounds. The sodium plumbite solution used in the industry is commonly referred to as doctor solution and consists principally of a solution of lead oxide, caustic soda and water in varying proportions according to the result desired.

In the process of sweetening petroleum prod ucts it is usually necessary to add elementary.

sulphur and this, together with the sulphur in the petroleum products, converts most of" the lead in the sodium plumbite into lead sulphide. The spent doctor solution which results after the conversion of the sulphur is a black sludge consisting principally of oil, lead sulphide, caustic soda and sodium sulphide. Becauseof the difiiculties which have been experienced in reclaiming the spent doctor solution the usual practice has been .to remove it as a waste product. This results in a serious economic loss and is also frequently a nuisance'as the lead sulphide contaminates any streams or bodies of water into which the waste doctor solution may be discharged. It has been proposed to reclaim and revivify the spent doctor solution by blowing compressed air through the solution. Without going into the details of the chemical reaction involved it may be stated that this aeration of the spent solution results in a conversion of the lead sulphide and caustic soda into sodium plumbite and water in substantially the same form as the solution before the reaction with the sulphur in the oil..

- with the spent solution and to inefliciencies" in the procedure followed.

Among the objects of our invention are: the provision of an improved method of treating spent doctor solution to reclaim and return it to its original condition; the provision of a 7 taken on line 2-2 of Figure, 1.

method of handling sodium plumbite or doctor solution in which the spent doctor solution may be revivifiedand used over and over again with a minimum of loss; the provision of a method Iof regenerating spent sodium plumbite in 5 which the oil in the spent solution is practically completely removed from. the solution thereby greatly increasing the efficiency of the process 7 and the percentage of lead sulphide which may be converted into sodium plumbite in a given 10,

being had ,to the accompanyingdrawings, in 15 which- V Figure 1 is a side elevationpartly in section of our improved mixing apparatus.

Figure 2 is a cross section, on a reduced scale,

7 Figure 3 is a diagrammatic side elevation of apparatus adapted to carry out our improved method of regenerating sodium plumbite.

In the drawings (Figures 1 and 2) the tank I is suitablyrmounted on a base or-foundation' 2 5 and'is provided with a top cover plate 3. The chimney 4 serves to carry away vapors which may arise from the liquid being treated in the tank. A vertical shaft 5 is centrally disposed in the tank I and may have a bearing at its lower 3 end in the bracket 6. The upper-end of the shaft 5 is connected to the driving motor, or other prime mover 1 through the gear box 8, which in the illustration shown is'adapted to transmit power at right angles, and the belt or chain 9 which connects the pulley or sprocket Hi to the motor 1. A second belt or chain l I is' adapted to 'drive the blower fan l2 from the motor I. This fan l2 may be of any suitable type. and takes air from the atmosphere and causes it to flow at relatively low pressure, downwardly through a pipe 13 into the tank l. The lower end of the pipe l3, as shown, comprises an annular outlet member M which isprovided with a plurality of holes on its lowercside; Thedrive shaft- 5 passes through the central opening in the annular outlet M;

housing It for: the. impellerliiis supported by lugs llwhich are clamped on or otherwise suitablyattachedto the vertically extending rods w, 5

The housing [6 is provided with annular top and bottom inlet openings I9 and 20 and with a slotlike circumferentially extending outlet opening 25. As seen in Figure 1 this outlet opening 2! is adapted to discharge fluid in a downwardly direction as indicated by the arrows on the drawings.

Another agitating impeller 22 is mounted on the shaft 5 below the impeller I5. This impeller 22 is substantially the same as impeller [5 but the impeller housing 23 is provided with split circumferentially extending outlet slots 24 and E5 and it will be seen that fluid which is drawn in through the inlet openings by the rotation of the impeller 22 will be divided and part directed upwardly through the outlet slot 24 and. part downwardly through the outlet slot 25. The impellers l5 and 22 are preferably vertically adjustable on the shaft 5 and the housings 23 and it may also be moved vertically on the rods l8. Thus, the agitating units may be spaced to give the most eifective operation and it will be understood by those skilled in the art that any desired number of agitating units may be mounted on shaft 5 as deemed necessary or desirable.

In order to maintain the liquid being treated at the proper temperature we have provided a pipe coil 26. Steam may be admitted to this coil through the pipe 21 and discharged either directly into the sewer connection 28 through the pipe 29 or by-passed into the sewer through the seam trap 30 by means of proper manipulation of the control valves 3| and 32.

The liquid to be treated (spent doctor solution) is conveyed to the tank I through the pipe 33 and a valve 35 is interposed in the pipe to control the flow therethrough. Another inlet pipe 323, having a valve 31, may be provided to supply water to the tank I to maintain the proper concentration of the solution.

A bottom outlet 38 controlled by a valve 39 is adapted to discharge the contents of the tank I into the sewer 28 through pipe 40. The pipe 40 is also connected through pipe 4|, valve 42 and pipe 43 to the pivoted skimmer pipe 44. This pipe 44 may be secured in the desired position by means of a chain 45 which engages a suitable hook 46 on the side of the hand hole 31 in the cover plate 3. The function of the skimmer pipe 44 will be later explained.

The regenerated doctor solution may be withdrawn from the tank I through the pipe 48 which extends into the tank I and has an inlet opening adjacent the bottom of the tank. The pipe 48 may be connected toa suitable pump or other means for withdrawing the liquid and the flow through the pipe can be controlled by the valve 49.

If desired the liquid which is skimmed off by the skimmer pipe 44 may be conducted to the pipe 48 through pipe '50 instead of discharging it into the sewer through the pipes 4| and 40. By proper manipulation of the valves 42 and 5| the disposal of the skimmed liquid may be controlled.

In Figure 3 we have diagrammatically illustrated a layout of apparatus adapted to carry out our improved method of regenerating sodium plumbite. In this layout the agitating unit which is generally indicated at A, is substantially the same as that illustrated in Figures 1 and 2 and described above. It should be noted, however, that the unit A is driven by a steam turbine55, as distinguished from the electric motor 1, shown in Figure land the piping arrangements are not treated, is collected in the tank 56.

exactly the same. These difierences will become evident from the following description of Figure 3.

The spent doctor solution, after it has been used to sweeten the oil, is discharged into the storage tank and may be kept at the desired 5 temperature therein by the steam coil 57 which may be supplied with steam from the pipe 58 under the control of valve 59. A pivoted skimmer pipe as is'disposed within the tank 56 and is adapted to skim ofi any oil which may rise to the 10 surface of the spent solution during its stay in the tank 56. This oil may be conducted through the pipes 6! and 62 to the wash oil tank 63. The spent solution is withdrawn from the bottom of the tank 55 through the pipe M by the transfer 15 pump 55. This pump 65 is adapted to force the spent solution through pipes 66 andB'l into the agitating unit A. The skimmer pipe 68 of unit A is preferably pivoted so that the proper quantity may be removed and the skimmed oil is conveyed 20 to the tank E3 by gravity through the pipe 52. An oil by-pass pipe as is provided so that, if desired, the oil may be discharged into the sewer through pipe ill. The heating coils H of the unit A are supplied with steam through the pipe 72 25 from a suitable source of supply and are also adapted to utilize exhaust steam from the turbine 55 which is connected to the coil H through the pipe 13.

The pump 55 is connected to the caustic tank 14 30 through the pipes 55 and. i6 and is adapted to withdraw caustic solution (NaOI-I) from the tank 14 and discharge it into the agitator A through pipes 65 and 6'? for purposes which are fully described later. After the regenerating process has 5 been completed in the unit A the regenerated doctor solution is withdrawn from the lower part thereof through the pipe Ti. 7 The pump 65 is suitably connected to the pipe 'l'i through the pipe 78 and is adapted to withdraw the regenerated solution and discharge it through pipe 19 into the regenerated doctor solution storage tank Bli. The tank 80 is provided with a bottom outlet pipe 8! which conducts the solution to the treater where the oil is sweetened. In the layout above described it will be understood that valves are disposed wherever necessary to properly control the operation of the apparatus and are conventionally illustrated in the drawings. A single transfer pump 65 is so connected that it may be utilized to discharge the various fluids into the unit A and to withdraw the regenerated solution therefrom. Thus, by properly manipulating the control valves thepump can be connected to withdraw fluid from any one of the tanks 56, 63 and 14 and as throughthe pipe 15 and dis- 55 charge the liquid into the tank of the regenerating unit A through the pipes 65 and 67. i The water may be discharged into the unit A through the pipes 82 and 81.

Our improved method of regenerating the spent doctor solution will now be described, reference being had to the apparatus illustrated in Figure 3. a

The spent doctor solution; which always contains a certain amount of the oil which has been 65 While the solution remains in the tank 56 some of the oil may rise to the surface'thereof and be skimmed ofi through the pipe 58 and carried by gravity to the oil tank 'Io startthe operation, a charge of spent solution is'withdrawn from the tank 55 and discharged into the tank of unit A. As noted above a portion of the oil whichis contained in the spent solution may be separated out by simply heating the solution and allow ing the lead sulphide to settle and the oil to' rise to the surface Where it may be removed by skimming. However, a certain portion of the oil is combined with the sodium hydroxide and the lead sulphide in the form of emulsion which will not break up by simple settling and heating. Therefore, in our improved process'we heat the solution in the tank of unit A to the proper temperature, from approximately 150 F., to approximately 175 F., and by rotating the impellers of the unit A sufiiciently rapidly the mixture is violently agitated, breaking up the emulsionof oil and lead sulphide and causing the lead sulphide particles to be scrubbed by the sodium hydroxide in the solution and freed from the oil; After the emulsion is broken the agitation of the mixture is continued but with less intensity in order to coagulate the lead sulphide particles and cause them to settle and also to coagulate the particles of oil so that they can rise to the surface and be withdrawn by skimming.

So far as we are aware no satisfactory means for breaking up the emulsion of oil and lead sulphide has been proposed prior to our invention. As it is necessary that substantially all of the oil be removed from the solution before successful oxidization of the lead sulphide can take place Spent this step of our process is very important. doctor solution from .the treating of cracked distillates usually contains complex gums and tars and forms emulsion both in the water phase and in the oil phase. Simple heating will not break these complex emulsions. We are aware that some effort has been made to actually distill off the oil with superheated steam but it has been found that this operation costs more than the value of the recovered products and is not practical. It is also necessary to remove these complex tars and gums before regenerating the spent will be worthless.

The regenerator unit A provides a means for controlled agitation and heating by which the emulsion of the oil with the sodium hydroxide and lead sulphide may be broken and oil free lead sulphide be precipitated. If necessary, addition- The heating operation may now be continued' until the solution reaches a temperature of approximately 175 F. (this temperature, however, is subject to rather wide variation). Provisions are made for adding fresh sodium hydroxide (NaOH) solution to the regenerator unit A so that sodium plumbite may be formed as rapidly as the lead sulphide is oxidized to lead sulphate or lead oxide.

Next the motor or steam turbine l isstarted driving the impellers l5 and 22 and the blower fan l2. The rotation of the impeller causes the liquid to be drawn in through the inlet openings i9 and and discharged downwardly through the circumferential slot 2|. 7 into the liquid through the pipe l3 and the an-' nular outlet head l4 and, as the holes in the head I4 are immediately adjacent the inlet opening 29, a large part of the air will be drawn. down into the impeller l5 and. caused to be intimately mixed Air is blown with the liquid and discharged outwardly through the slot 2! and carried down into the tank with the liquid as indicated by the arrows. This downwardly moving body of mixed liquid and air is picked up by the impeller 22 and is again inti- 5 mately mixed and agitated and thrown out through the outlet openings'24 and 25. The mixture' which is discharged from the outlet 7 moves downwardly toward the bottom of the. tank; and will; to a considerable extent, swirl 10 around and beedrawn back into the bottom inlet opening to the impeller 22. 7 By providing 'a dual arrangement of impellers togetherwith the air inlet which is adapted to supply the air directly 7 into the inlet of one of the impellersan extreme- 15 ly thorough and complete mixture and agitation of the liquid with'the air is effected. 'The airis retained'in the solution for a relatively long period of time with the result that very efiicient oxidization is accomplished.

In the operation of our apparatus we have found that 90 to 95% of lead sulphide may easily be converted into sodium plumbite ina period of eight to ten hours. Afterthe regeneration is completed the tank contains a clear sodium plum- 5 bite or doctor solution which is ready for use and equal in its effectiveness tofresh doctor solution.

Frequently the regenerated doctor solution contains oil soluble impurities which, if permit- 3 ted to remain in the solution, would discolor oil being treated thereby. These impurities can be removed by washing the solution with oi1.- As the oil which is skimmed from thespent doctor solution in the unit A is accumulated in the tank 63, and as this oil has already been sweetened, it is available for washing the regenerated doctor solution. Therefore, if it is necessary r to wash the regenerated doctor solution, a pordoctor solution or else the resultant sodium plumbite solution will be so contaminated that it tion of the skimmed oil is pumped to the regen- 40 erating unit A from the tank 63 through the pipes 66 and 61, after the regeneration reaction is 'finished, and is agitated together with the regenerated doctorsolution. After the washing action is completed the agitating impellers are stopped and the oil allowed to rise to the surface from whence it is skimmed and either carried to the refinery to be redistilled or discharged to waste.

7 The above described oil washing of the regener ated doctor solution removes colored impurities and free sulphur and leaves the regenerated doctor solution equal to fresh doctor solution.

The air pressure necessary to draw the air into. the liquid need be very small and the power re-' quired by the blower fan. I2 is negligible. In some cases the blower l2 may be omitted entirely as sufficient air will be drawn into the liquid" through the pipe l3 from the atmosphere due to the suction of the impeller [3 which is effective at the inlet opening 20. 1

It will be seen from the above description of one form of our apparatus and our process'for regenerating doctor solution that the regeneration cycle, including the steps of breaking the emulsion, oxidizing and oil' washing of the regenerated solution is completed in a single unit. With" our process we are able to return a high percentage of the spent sodium plumbite solution to useable form.

Although we have illustrated and described in fled-forms and arrangements of apparatusmay be used to carry out our process. Further, it will be understood by those skilled in the art that our regenerating process may be modified without departing from the spirit of our invention. We do not, therefore, limit ourselves to the specific steps of our method but claim as our invention all embodiments thereof coming within the scope of the appended claims.

We claim:

1. The method of regenerating spent sodium plumbite which includes the steps of heating a body of spent solution and subjecting said solution to relatively violent and then relatively gentle agitation to break up the emulsion therein and coagulate the oil whereby said oil may rise to the surface of the mixture, skimming off the oil so separated, discharging air into the remaining spent solution and intimately mixing and maintaining said air in contact with said solution, continuing such agitation and mixture of the solution with air until the regenerating reaction is completed.

2. In the regeneration of spent doctor solution the method which includes the steps of heating a body of spent solution and subjecting said solution to relatively violent and then relatively gentle agitation to break up the emulsion therein and coagulate the lead sulphide and the oil whereby said oil may rise to the surface of the mixture, skimming off the oil so separated, directing air into the spent solution, breaking up the air into finely disseminated condition in said solution and positively causing said body of solution to circulate in a manner to maintain the air in the solution and intimately mix it therewith, continuing such agitation and mixture of the solution with air until the regenerating reaction is completed.

3. In the regeneration of spent doctor solution the method which includes the steps of heating a body of spent solution and subjecting said solution to a violent agitation and scrubbing action to break the emulsion therein, subjecting the solution to a further relatively gentle agitation to coagulate the lead sulphide particles and the oil particles separated therefrom whereby the lead sulphide particles will settle and the oil particles will rise to the surface of the mixture, skimming off the oil so separated, maintaining the solution at approximately 175 F., directing an oxygen containing gas into the oil free solution, breaking up the gas into finely disseminated condition in said solution'and positively causing said body of said solution to circulate in a manner to maintain the gas in the solution and intimately mix it therewith, continuing such agitation and mixture of the solution with the gas until the regenerating reaction is completed, adding sweetened washing oil to the regenerated solution and agitating the mixture to remove oil soluble discoloring impurities and then removing the wash oil from the solution.

FREDERICK W. STONE.

JAMES N. GARRISON. 

